An organic electroluminescent device is a novel flat panel display device, and compared with a liquid crystal display (LCD), has characteristics, such as high brightness, active luminescence, a wide view angle, a fast response speed, etc., which is a rising star in the field of a flat panel display, and shows wide development and application prospects. A light emitting principle of the organic electroluminescent device is that carriers are injected from electrodes into a light emitting layer by an external electric field to recombine so as to emit light. The organic electroluminescent device requires an anode material to have a high work function and a good light transmissivity to facilitate emission of the light from the device.
Currently, the anode material of the organic electroluminescent device generally adopts In2O3 doped with SnO2 (In2O3:SnO2), i.e., ITO. The ITO has a conduction band mainly composed by 5 s orbitals of In and Sn, and a valence band having an 2p orbital of oxygen occupying a dominant position, and oxygen vacancies and Sn4+ ions replacing dopant atoms form a donor level and affect a carrier concentration in the conduction band. Since the oxygen vacancies and Sn4+ ions replacing doped In3+ ions, which are generated in an ITO thin film, form a highly degenerated n-type semiconductor during deposition of ITO, and an Fermi level EF is located above a bottom of the conduction band EC, ITO has a very high carrier concentration and a low resistivity. In addition, ITO has a relatively wide band gap, and thus the ITO thin film has a very high transmittance for visible light and near infrared light. Since ITO has the above excellent conductivity and light transmission, it is widely used as an anode electrode in an electro-optoelectronic device such as a liquid crystal display (LCD), an organic electroluminescent light emitting diode (OLED), a quantum dot light emitting diode (QLED) and a solar cell (OPV).
Although an ITO electrode has the above series of advantages, since ITO belongs to a non-stoichiometric compound, a chemical composition on a surface of the ITO thin film has a great influence on a work function of the surface thereof. The work function of ITO has a work function of 4.5-5.0 eV, which is still low compared with metals such as Ni (5.4 eV), and thus is not good for injection of holes. Meanwhile, since the ITO thin film is very flimsy, it is very easily to be damaged even subjecting to bending of a relatively small physical stress, and the ITO thin film has a poor flex resistance. However, the current deformable and flexible display device and the current flexible electroluminescent device have become the mainstream direction of the future market. Therefore, in the tide of the emerging product market where wearable equipments are gradually rising, the ITO material as a conductive electrode has been unable to meet the requirements of the market, and is gradually eliminated.
On this basis, it is necessary to provide a transparent conductive anode having a high work function and suitable for a flexible light emitting device to replace the ITO.